The present invention relates to a displacement detection apparatus and a displacement detection method for detecting displacement of a detection target.
Displacement detection sensors known in the art as sensors for detecting displacement of a detection target include displacement detection sensors of self-oscillating type and displacement detection sensors of resonance type, which detect change in distance from the target in the form of changes in oscillation intensity and oscillation frequency originating in eddy current produced in the target. A displacement detection sensor of self-oscillating type produces oscillation by means of an inductor, directs the magnetic flux output by the inductor against the target, and detects change in distance from the target from changes in oscillation intensity and oscillation frequency. Accordingly, when several self-oscillating displacement detection sensors are situated adjacently, oscillation conditions may be affected by flux output by other adjacently situated self-oscillating displacement detection sensors, resulting in inability to accurately sense changes in oscillation intensity. In order to prevent this, interposition of magnetic shielding has been contemplated, but this is associated with higher costs, and it is difficult to achieve complete shielding.
A displacement detection sensor of resonance type, on the other hand, obtains by means of a crystal oscillator or other such external oscillator a frequency to be superimposed on a drive voltage, and drives a resonance circuit. In this case, since the oscillation frequency produced by the external oscillators is the same, even when magnetic flux is output from individual inductors, the effects on adjacent circuits is lessened. Relevant publications include Unexamined Patent Application 2003-298403 and Unexamined Patent Application 9-101106.